It is common in telecommunications systems to rely on card cages that are secured in standardized racking systems. Pre-determined specifications define the height and other dimensions of the enclosures for these card cages so that equipment provided by various manufacturers may be readily used in combination in standard racks. Some example standards for dimensioning include, but are not limited to, AMC, ARINC, ATCA, cPCI, MicroTCA, VME, and VME 64. These standards are defined by various industry standards organizations including ANSI, IEEE, PICMG, VITA, as well as others including military organizations. A the electronics cards that are mounted in the card cages generate heat during their operation, appropriate amounts of cooling airflow are provided to carry the heat away from the operating equipment.
North American data centers and telecommunication companies are increasingly demanding that central office equipment incorporate front to back cooling solutions, wherein cooling air is drawn in from the front of the cabinet and exhausted to the rear. This allows the service provider to set up more manageable HVAC (Heating, Ventilating, and Air Conditioning) environments with cooler (front) maintenance aisles and warmer (rear) wiring aisles.
This requirement causes implementation challenges with smaller sized products and enclosures that are typically designed with horizontal cards using side-to-side cooling. Front to back air cooled systems require significantly more rack height, due to larger cooling intake and exhaust requirements and typically require cards to be installed vertically or limit the thermal load of horizontal cards.
Referring to FIG. 1, there may be seen a typical Central Office Small Box card cage assembly 100 has rack mounting flanges 102 according to the prior art. Circuit cards 104 are mounted within card cage assembly 100. Fans 106 induce cooling air flow to pass through card cage assembly 100 and circuit cards 104, with the cooling air entering on the fan side of card cage assembly 100 and exiting the opposite side.
Referring to FIG. 2, there may be seen an alternate solution according to the prior art, wherein front to back airflow is achieved at the expense of additional vertical rack space. Card cage assembly 200 has been rotated by 90 degrees from the orientation shown in FIG. 1, and again has circuit cards 204 mounted within card cage assembly 200 and fans 206. Large intake baffles 208 are located at the bottom of the card cage assembly 200, and corresponding large exhaust baffles 210 are located at the top of the chassis. Cooling air flow enters at the front of card cage assembly 200 through intake baffles 208, is accelerated by fans 206, and proceeds vertically through card cage assembly 200, passing circuit cards 204 and cooling them thereby. The heated air exits exhaust baffles 210 at the top of the card cage assembly 200 and is directed to the rear of the rack. By way of example, in FIG. 2 the 10.5″ tall Small Box card cage assembly 200 in this configuration requires approx. 26.3″ of rack height to provide sufficient intake and exhaust openings. In space constrained central offices this additional vertical height requirement is not a preferred arrangement from the operator's perspective.
Referring now to FIGS. 3A and 3B, there may be seen yet another prior art method of routing cooling air through a card cage assembly. FIG. 3A provides an elevation view of this configuration from the front of the equipment rack. Central Office Small Box card cage assembly 300 has rack mounting flanges 302 according to the prior art. Circuit cards 304 are mounted within card cage assembly 300. Fans 306 induce cooling air flow to pass through card cage assembly 300 and circuit cards 304, with the cooling air entering opposite to the fan side of card cage assembly 300 at 308 and exits after passing through the fan assembly 306 at exhaust 310. FIG. 3B is a view of this configuration from the top. Cooling air enters from the front at 308, passes through the equipment cards 304, passes through the fan assembly 306, and exits via the rear exhaust 310. In this configuration cooling air must navigate several sharp turns—as it enters the intake baffles and then turns 90° to flow through the cards 304, and then upon exiting the fan assembly 306 it then turns a further 90° to flow through the rear exhaust 310. These changes in air direction result in pressure head loss, limiting the amount of cooling air that is provided by the system fans.
Therefore, there exists a need to overcome the drawbacks associated with the prior art as discussed above.